Thermodynamic sensors for detecting inclination and acceleration are known from DE 42 43 978 C1. Temperature-dependent electrical resistances of which at least one is heated are arranged in a closed fluid-filled capsule. The convective flow established in a gravitational or inertial field is evaluated.
EP 1 111 395 A1 and U.S. Pat. No. 6,722,199 B2 describe sensors for detecting rate of rotation, rotational acceleration and inclination based on the principle from DE 4243978 C1. Also known are other thermodynamic sensors wherein the temperature differences in the convective flow field are detected, for example, by thermoelements (thermopiles).
In these known sensors it is initially assumed that the measuring elements must adapt to the respective temperature of the isotherms in the convection field during an inclination or acceleration. Even if the mass of the measuring elements is small, this thermal adaptation takes a certain time. Thus, the response time of the sensors is frequently too high and the limiting frequency relatively low. In known sensors the signals for the inclination and acceleration cannot be directly discriminated.
Sensors based on density differences in fluids and methods for operating and for manufacturing said sensors are known from DE 103 48 245.8-52 of the applicant. Unlike previously described operating methods using sensor elements which adjust to a new temperature in a stationary isothermal field during a movement or change in position, in this case cyclic density fluctuations are generated by a transmitting element, received by a receiver and substantially time shifts (e.g., of the temperature variations) which are seen during movement or change in position are detected.
In claim 6 of the patent specification DE 42 43 978 C1 reference is already made to the possibility of regulating at least one of the temperature-dependent elements at constant temperature. No specific instruction as to how this operating variant can be advantageously used is found either in this patent specification nor in other relevant documents.
It is the object of this invention to describe the structure, operating mode and method of manufacture of fluid-filled thermodynamic sensors for detecting movement, acceleration and measured quantities attributable to acceleration where lateral and vertical acceleration, rate of rotation and rotational acceleration can be assigned and, under the action of acceleration due to gravity, a separate identification of position with respect to the perpendicular can be made. It is further the object of the invention to provide conditions for fast response, high limiting frequency, self-testing capability, independent after-calibration, monitoring of fluid density, best possible accuracy and long-term stability of said sensors.
The proposed sensors should be suitable for individual quantities or for a selection of or for all said quantities (inertial sensor) and preferably should be manufacturable using Microsystems technology.
When designing the sensors, broadly all acting forces and effects (inertia, Earth's attraction, centrifugal acceleration, Coriolis effect etc.) should be taken into account.
The operating modes should be described including specific circuits.